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From: Andrew Turner <andrew@FreeBSD.org>
Date: Mon, 25 Apr 2016 17:32:09 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r298586 - head/sys/arm64/include
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Author: andrew
Date: Mon Apr 25 17:32:08 2016
New Revision: 298586
URL: https://svnweb.freebsd.org/changeset/base/298586

Log:
  Use the yield instruction in the arm64 cpu_spinwait. This instruction is
  a hint to the hardware the software is not performing a task.
  
  Sponsored by:	ABT Systems Ltd

Modified:
  head/sys/arm64/include/cpu.h

Modified: head/sys/arm64/include/cpu.h
==============================================================================
--- head/sys/arm64/include/cpu.h	Mon Apr 25 17:06:50 2016	(r298585)
+++ head/sys/arm64/include/cpu.h	Mon Apr 25 17:32:08 2016	(r298586)
@@ -50,7 +50,7 @@
 
 #define	cpu_getstack(td)	((td)->td_frame->tf_sp)
 #define	cpu_setstack(td, sp)	((td)->td_frame->tf_sp = (sp))
-#define	cpu_spinwait()		/* nothing */
+#define	cpu_spinwait()		__asm __volatile("yield" ::: "memory")
 
 /* Extract CPU affinity levels 0-3 */
 #define	CPU_AFF0(mpidr)	(u_int)(((mpidr) >> 0) & 0xff)